Power transmission system for use in vehicle

ABSTRACT

The power transmission system for use in a vehicle includes a power split device to perform power distribution among a flywheel for storing rotational energy as mechanical energy, an internal combustion engine and an electric rotating machine. The power transmission system is provided with an interrupting device configured to interrupt power transmission between a group of the flywheel and the electric rotating machine and a group of the internal combustion engine and drive wheels of the vehicle when rotational energy stored in the flywheel is transmitted to the electric rotating machine through the power split device under condition that power is transmitted between the internal combustion engine and the drive wheels.

This application claims priority to Japanese Patent Application No.2009-254231 filed on Nov. 5, 2009, the entire contents of which arehereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a power transmission system for use ina vehicle including a power split device which performs powerdistribution among a flywheel for storing rotational energy asmechanical energy, an internal combustion engine and an electricrotating machine.

2. Description of Related Art

As such a power transmission system, there is the one in which aplanetary gear device performs power distribution of the power between atransmission coupled to drive wheels and an internal combustion engine,the power of a flywheel, and the power of an electric rotating machine.For example, refer to International Patent Application Publication No.WO 2009/010819. According to this system, it is possible to store torqueof the drive wheels in the flywheel or the electric rotating machinethrough the transmission.

However, the above conventional system has a problem in that it mayoccur that a vehicle-mounted battery cannot be charged properly byelectric energy which the electric rotating machine generates byconverting the rotational energy stored in the flywheel into electricenergy while the vehicle runs, because the conversion by the electricrotating machine is affected by the rotational speed of the drivewheels.

SUMMARY OF THE INVENTION

The present invention provides a power transmission system for use in avehicle comprising:

a power split device to perform power distribution among a flywheel forstoring rotational energy as mechanical energy, an internal combustionengine and an electric rotating machine; and

an interrupting device to interrupt power transmission between a groupof the flywheel and the electric rotating machine and a group of theinternal combustion engine and drive wheels of the vehicle whenrotational energy stored in the flywheel is transmitted to the electricrotating machine through the power split device under condition thatpower is transmitted between the internal combustion engine and thedrive wheels.

The present invention also provides a power transmission system for usein a vehicle comprising:

a first power split device including a first rotating body mechanicallycoupled to a first electric rotating machine, a second rotating bodymechanically coupled to drive wheels of the vehicle and a third rotatingbody mechanically coupled to an internal combustion engine of thevehicle, and configured to perform power distribution among the firstelectric rotating machine, the drive wheels and the internal combustionengine; and

a second power split device including a fourth rotating bodymechanically coupled to a flywheel for storing rotational energy asmechanical energy, a fifth rotating body mechanically coupled to asecond electric rotating machine, and a sixth rotating body mechanicallycoupled to one of the first to third rotating bodies of the first powersplit device to perform power distribution among the flywheel, thesecond electric rotating machine and the first power split device.

According to the present invention, there is provided a powertransmission apparatus for use in a vehicle of the type including apower split device to perform power distribution among a flywheel tostore rotational energy as mechanical energy, an internal combustionengine and an electric rotating machine, which is capable of properlycharging a vehicle battery using rotational energy stored in theflywheel to thereby make an effective use of regenerative energy.

Other advantages and features of the invention will become apparent fromthe following description including the drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1A is a diagram showing the structure of a power transmissionsystem for use in a vehicle according to a first embodiment of theinvention;

FIG. 1B is a diagram showing the cross-sectional structure of a powersplit device included in the power transmission system;

FIGS. 2A to 2F are collinear diagrams of rotational speeds of rotatingbodies included in the power split device of the power transmissionsystem;

FIG. 3 is a diagram showing the structure of a power transmission systemfor use in a vehicle according to a second embodiment of the invention;

FIG. 4 is a diagram showing the structure of a power transmission systemfor use in a vehicle according to a third embodiment of the invention;

FIG. 5 is a diagram showing the structure of a power transmission systemfor use in a vehicle according to a fourth embodiment of the invention;

FIG. 6 is a diagram showing the structure of a power transmission systemfor use in a vehicle according to a fifth embodiment of the invention;

FIG. 7 is a diagram showing the structure of a power transmission systemfor use in a vehicle according to a sixth embodiment of the invention;

FIGS. 8A and 8B are diagrams showing the structure of a powertransmission system for use in a vehicle according to a seventhembodiment of the invention;

FIGS. 9A to 9E are collinear diagrams of rotational speeds of rotatingbodies included in a power split device of the power transmission systemaccording to the seventh embodiment of the invention;

FIGS. 10A and 10B are collinear diagrams of the rotational speeds of therotating bodies when the power transmission system of the seventhembodiment is in a regenerative control mode;

FIG. 11 is a flowchart showing a control process performed by the powertransmission system of the seventh embodiment during the regenerativecontrol mode;

FIGS. 12A and 12B are collinear diagrams of the rotational speeds of therotating bodies when the power transmission system of the seventhembodiment is in an EV-running mode;

FIG. 13 is a flowchart showing a control process performed by the powertransmission system of the seventh embodiment during the EV-runningmode; and

FIGS. 14A to 14D are collinear diagrams of the rotational speeds of therotating bodies included in the power split device of the powertransmission system according to the seventh embodiment of theinvention.

PREFERRED EMBODIMENTS OF THE INVENTION First Embodiment

FIG. 1A is a diagram showing the structure of a power transmissionsystem for use in a vehicle according to a first embodiment of theinvention.

The first embodiment describes an application of the present inventionto a vehicle having an internal combustion engine 10 as a single mainengine thereof. A crankshaft 10 a of the engine 10 is mechanicallycoupled to drive wheels 16 through a transmission 12 and a differential14. The crankshaft 10 a is provided with a starter 18 as a means toprovide initial rotation to the crankshaft 10 a.

The crankshaft 10 a is mechanically coupled to a power split device 24through a clutch 20 and a locking device 24 at its end not coupled tothe transmission 12. The power split device 24 includes a plurality ofrotating bodies which rotate in conjunction with one another, anddistribute power among the engine 10, the flywheel 30 and an alternator32. In more detail, the power split device 24 is constituted of a singleplanetary gear device having a sun gear S mechanically coupled to theflywheel 30, a carrier C mechanically coupled to the engine 10, and aring gear R mechanically coupled to the alternator 32. FIG. 1B shows thecross-sectional structure of the power split device 24.

The flywheel 30 serves as an energy storing means to store rotationalenergy inputted thereto as kinetic energy. The alternator 32, whichserves as electric power generating means, has a function as a powersource for vehicle-mounted accessories including the starter 18, and afunction of discharging an auxiliary battery 36. The clutch 20 serves asan interruption means to interrupt power transmission between the engine10 and the power split device 24 (carrier C) by disengaging themechanical coupling between the engine 10 and the carrier C of the powersplit device 24. The locking device 22 is a device capable of inhibitingthe carrier C as a rotating body coupled to the engine 10 to rotate. Alocking device 26 is a device capable of inhibiting the sun gear S as arotating body coupled to the flywheel 30 to rotate. A clutch 28 servesas an interruption means to interrupt power transmission between theflywheel 30 and the power split device 24 (sun gear S) by disengagingthe mechanical coupling between the flywheel 30 and the sun gear S ofthe power split device 24.

A control apparatus 34 is for controlling the vehicle. For example, thecontrol apparatus 34 controls a vehicle drive force by manipulating theengine 10, starter 18, clutch 20, locking devices 22 and 26, clutch 28,and alternator 32.

FIGS. 2A to 2F are collinear diagrams of the rotational speeds of thethree rotating bodies (sun gear S, carrier C and ring gear R) of thepower split device 24 controlled by the control apparatus 34 togetherwith the rotational speed of the engine 10. In FIGS. 2A to 2F, thearrows indicate the directions of torque. In these figures, thedirection of torque is positive when it points upward as well as thedirection of the rotational speed. Accordingly, the rotational energy isdefined to be positive when it enters the power split device 24. In thefollowing, FIGS. 2A to 2F are explained in this order.

FIG. 2A Showing a State in which the Vehicle is Stationary:

When the vehicle is stationary, and the rotational energy stored in theflywheel 30 is sufficient as shown in the section (i), this rotationalenergy is converted into electric energy by the alternator 32, andsupplied to the auxiliary battery 36. At this time, the engine 10 is inthe stopped state, and the clutch 20 shown in FIG. 1 is in thedisengaged state. Accordingly, the carrier C is inhibited from rotatingby the locking device 22. This is to apply torque to the carrier C asexplained in detail below.

In the planetary gear device, when the torque of the sun gear S is Ts,the torque of the carrier C is Tc, the torque of the ring gear R is Tr,the following equations (c1) and (c2) hold.

Tr=−Tc/(1+ρ)  (c1)

Ts=−ρTc/(1+ρ)  (c2)

In the above equations, ρ(=Zs/Zr) is the ratio of the gear number Zr ofthe ring gear R to the gear number Zs of the sun gear S. As seen fromthe above equations, when the locking device 22 is not in the lockedstate, since the torque Tc of the carrier C is 0, the ring gear R andthe sun gear S are not applied with torque. As a result, torquetransmission between the ring gear R and the sun gear S is disabled. Onthe other hand, when the carrier C is locked by the locking device 22,it is possible to control the rotational energy transmitted from theflywheel 30 to the alternator 32 by controlling the torque which thealternator 32 applies to the ring gear R. The rotational speeds of thesun gear 5, carrier C and ring gear R are in a linear relationship.Accordingly, when the rotational speed of the carrier C is fixed at 0,the speed of the alternator 30 (ring gear R) is uniquely determineddepending on the rotational speed of the flywheel 30 (sun gear 5).

On the other hand, if the rotational speed of the flywheel 30 is 0 whenthe vehicle is stationary, all the three rotating bodies of the powersplit device 24 are in the stopped state as shown in the section (ii).

FIG. 2B Showing a State in which the Engine 10 is Started:

When the rotational energy of the flywheel 30 is sufficient at the timeof starting the engine 10 as shown in the section (i), an initialrotation is provided to the crankshaft 10 a of the engine 10 using therotational energy of the flywheel 30 without using the starter 18. Atthis time, power generation control of the alternator 32 is performed.This is for enabling power transmission through the power split device24 in accordance with the above equations (c1) and (c2).

On the other hand, when the rotational energy of the flywheel 30 isinsufficient at the time of starting the engine 10 as shown in thesection (ii), the engine 10 is started using the starter 18. At thistime, the power generation control of the alternator 32 is notperformed. Accordingly, power transmission through the power splitdevice 24 is not performed. The clutch 28 is put in the disengagedstate, and the sun gear S is locked by the locking device 26 at thistime. This is for preventing a difference in rotational speed betweenthe input and the output of the clutch 28 from becoming excessive at thetime of putting the clutch 28 in the engaged state. Alternatively, it ispossible that the clutch 28 is put in the engaged state, and the lockingdevice 26 is put in the unlocked state.

FIG. 2C Showing a State in which the Vehicle Starts Moving or RunningUnder Light Load:

When the rotational energy stored in the flywheel 30 is sufficient whenthe vehicle starts moving, or running under light load (EV-running) asshown in the section (i), the vehicle runs using the rotational energyof the flywheel 30 without using the engine 10. At this time, since thering gear R is applied with torque by performing the power generation ofthe alternator 32, power transmission through the power split device 24is enabled.

On the other hand, when the rotational energy stored in the flywheel 30is insufficient as shown in the section (ii), the sun gear S is lockedby the locking device 26, so that the vehicle runs by the drive power ofthe engine 10 while the power generation control of the alternator 32 isperformed. The reason why the lock device 26 is used at this time is toenable power transmission through the power split device 24 in a statewhere the rotational energy of the engine 10 is prevented from beingsupplied to the flywheel 30, and also enable performing the powergeneration control of the alternator 32. If the locking device 26 is notused, part of the rotational energy of the engine 10 is supplied to theflywheel 30. Incidentally, when the power generation control of thealternator 32 is not performed, the sun gear S might not be locked bythe locking device 26. This is because power transmission through thepower split device 24 is disabled in this case.

FIG. 2D Showing a State in which the Vehicle Runs Steadily:

To store rotational energy in the flywheel 30 while the vehicle runssteadily as shown in the section (i), the alternator 32 is caused togenerate power while the engine 10 runs. At this time, generating powerby the alternator 32 is integral to transmit the rotational energy ofthe engine 10 to the flywheel 30 through the power split device 24.

On the other hand, when any of energy storing in the flywheel 30 andenergy releasing from the flywheel 30 is not performed as shown in thesection (ii), the vehicle runs by the drive force of the engine 10 withthe sun gear S being locked by the locking device 26 while performingthe power generation control of the alternator 32. The reason why thelocking device 26 is used at this time is to enable power transmissionthrough the power split device 24 in a state where the rotational energyof the engine 10 is prevented from being supplied to the flywheel 30,and also enable performing the power generation control of thealternator 32. Incidentally, when the power generation control of thealternator 32 is not performed, the sun gear S might not be looked bythe locking device 26. This is because transmission through the powersplit device 24 is disabled in this case.

Further, when the energy stored in the flywheel 30 is converted intoelectric energy by the alternator 32 while the vehicle runs using thedrive force of the engine 10 as shown in the section (iii), the powergeneration control of the alternator 32 is performed in a state wherethe carrier C is locked by the locking device 22. At this time, theclutch 20 is put in the disengaged state to interrupt power transmissionbetween the engine 10 and the power split device 24. The reason why thecarrier C is locked by the locking device 22 is to enable the rotationalenergy of the flywheel 30 to be transmitted to the alternator 32 throughthe power split device 24.

FIG. 2E Showing a State in which the Vehicle Accelerates:

To use the rotational energy of the flywheel 30 in addition to therotational energy of the engine 10 when the vehicle accelerates as shownin the section (i), the power generation control of the alternator 32 isperformed. Performing the power generation control of the alternator 32is necessary to transmit the rotational energy of the flywheel 30through the power split device 24.

On the other hand, when the rotational energy of the flywheel 30 is notused as shown in the section (ii), the vehicle runs using the rotationalenergy of the engine 10 in a state where the sun gear S is locked by thelocking device 26, and the power generation control of the alternator 32is performed. The reason why the locking device 26 is used at this timeis to enable energy transmission through the power split device 24.Accordingly, if the power generation control of the alternator 32 isstopped, the sun gear S might not be locked by the locking device 26.

FIG. 2F Showing a State in which Regeneration is Performed:

During a regeneration period, the engine 10 is stopped, and the powergeneration control of the alternator 32 is performed. As a result, therotational energy inputted to the carrier C is distributed to theflywheel 30 and the alternator 32 through respectively the sun gear Sand the ring gear R.

The first embodiment described above provides the following advantages.

(1) This embodiment includes the clutch 20 which interrupts powertransmission between the power split device 24 and the engine 10 whenthe rotational energy of the flywheel 30 is transmitted to thealternator 32 through the power split device 24 under condition wherepower transmission is performed between the engine 10 and the drivewheels 16 of the vehicle.

This makes it possible to effectively convert the rotational energy ofthe flywheel 30 into electric energy.

(2) This embodiment includes the locking device 22 which locks thecarrier C coupled to the engine 10. This enables transmission ofrotational energy through the power split device 24 even when the clutch20 is in the disengaged state 20.

(3) This embodiment includes the clutch 28 which disengages mechanicalcoupling between the sun gear S and the flywheel 30. This makes itpossible to interrupt power transmission between the power split device24 and the flywheel 30.

(4) This embodiment includes the locking device 26 which locks the sungear S coupled to the flywheel 30.

This enables power transmission through the power split device 24 evenwhen the clutch 20 is in the disengaged state 20.

(5) The crankshaft 10 a of the engine 10 is mechanically coupled to thepower split device 24 at one end thereof not connected to the drivewheels 16. This makes it possible to simplify the system structurecompared to a case where the power split device 24 is mechanicallycoupled in between the engine 10 and the drive wheels 16.

(6) This embodiment includes the power split device 24, and thealternator 32 as an electric rotating machine mechanically coupled tothe power split device 24.

This makes it possible to increase energy usage efficiency in thevehicle having the engine 10 as its sole main engine.

Second Embodiment

Next, a second embodiment of the invention is described with particularemphasis on the difference with the first embodiment.

FIG. 3 is a diagram showing the structure of a power transmission systemfor use in a vehicle according to a second embodiment of the invention.In FIG. 3, the reference numerals identical to those in FIG. 1 representthe same elements.

As shown in FIG. 3, in this embodiment, the starter 18 is mechanicallycoupled to the ring gear R. When the engine 10 is started without usingthe rotational energy of the flywheel 30, this makes it possible todrive the starter 18 to provide an initial rotation to the engine 10 ina state where the sun gear S is locked by the locking device 26. Therotational speeds of the ring gear R and the carrier C are the same asthose shown in the section (ii) of FIG. 2B.

The second embodiment provides the following advantage in addition tothe advantages (1) to (6) provided by the first embodiment.

(7) The starter 18 is mechanically coupled to the ring gear R coupled tothe alternator 32. As a result, since the rotational energy inputted tothe ring gear R coupled to the alternator 32 can be made positive byputting the starter 18 into operation, it is possible to improve energyusage efficiency by expanding the possible rotational speed range of thering gear R during energy regeneration, for example.

Third Embodiment

Next, a third embodiment of the invention is described with particularemphasis on the difference with the first embodiment.

FIG. 4 is a diagram showing the structure of a power transmission systemfor use in a vehicle according to a third embodiment of the invention.In FIG. 4, the reference numerals identical to those in FIG. 1 representthe same elements.

As shown in FIG. 4, in this embodiment, between the power split device24 and the flywheel 30, there is provided a step-up device 40 whichincreases the rotational speed of the power split device 24. The step-updevice 40 is constituted of a planetary gear device whose carrier C ismechanically coupled to the power split device 24, whose sun gear S ismechanically coupled to the flywheel 30, and whose

ring gear R is locked.

The third embodiment provides the following advantage in addition to theadvantages (1) to (6) provided by the first embodiment.

(8) Between the ring gear R coupled to the flywheel 30 and the flywheel30, there is interposed the step-up device 40. This makes it possible tomake the flywheel 30 compact in size for the same energy storingcapacity compared to the case where the step-up device 40 is notprovided.

Fourth Embodiment

Next, a fourth embodiment of the invention is described with particularemphasis on the difference with the first embodiment.

FIG. 5 is a diagram showing the structure of a power transmission systemfor use in a vehicle according to a fifth embodiment of the invention.In FIG. 5, the reference numerals identical to those in FIG. 1 representthe same elements.

As shown in FIG. 5, in this embodiment, the power split device 24 ismechanically coupled to the rotating shaft coupling the engine 10 to thetransmission 12. In this embodiment, the power between the engine 10 andthe drive wheels 16, the power of the flywheel 30 and the power of thealternator 32 are distributed by the power split device 24. Further, inaddition to the clutch 20, there is disposed a clutch 42 whichdisengages mechanical coupling between the engine 10 and thetransmission 12.

According to the fourth embodiment, other than the above advantages (1)to (6) provided by the first embodiment, the following advantage can beobtained.

(9) The power split device 24 is mechanically coupled in between theengine 10 and the drive wheels 16.

This makes it possible to transmit regenerated energy to the flywheel 30or alternator 32 without through the engine 10.

Fifth Embodiment

Next, a fifth embodiment of the invention is described with particularemphasis on the difference with the first embodiment.

FIG. 6 is a diagram showing the structure of a power transmission systemfor use in a vehicle according to a fifth embodiment of the invention.In FIG. 6, the reference numerals identical to those in FIG. 1 representthe same elements.

As shown in FIG. 6, in this embodiment, the ring gear R coupled to thealternator 32 is further coupled to vehicle-mounted accessories. Moreprecisely, the ring gear 32 is further mechanically coupled to acompressor 44 and a vacuum pump 45 of a vehicle air conditioner. Thevacuum pump 45 is mechanically coupled to the ring gear R through aclutch 46. The vacuum pump 45 is for reducing the pressure in the spacebetween the housing of the flywheel 30 and the ring gear R in order toreduce the air resistance which the flywheel 30 receives.

According to the above structure, it is possible to assist the torquewhich the alternator 32 applies to the ring gear R by the vacuum pump 45when it is not possible to sufficiently transmit regenerative energy tothe power split device 24 because of torque constraints of thealternator 32 although the regenerative energy is sufficiently large.Accordingly, according to the above structure, an amount of rotationalenergy inputted to the flywheel 30 per unit time can be increased.

Incidentally, when the torque required to be applied to the ring gearRat the time of recovering regenerative energy is smaller than themaximum output torque of the alternator 32, the clutch 46 may be putinto the disengaged state to interrupt power transmission from the powersplit device 24 to the vacuum pump 45.

According to the fifth embodiment, other than the above advantages (1)to (6) provided by the first embodiment, the following advantages can beobtained.

(10) The ring gear R coupled to the alternator 32 is coupled tovehicle-mounted accessories other than the alternator 32. This makes itpossible to use the ring gear R as a drive power source for thevehicle-mounted accessories.

(11) The above vehicle-mounted accessories include the vacuum pump 45 toreduce the pressure inside the housing of the flywheel 30. This makes itpossible to recover the regenerative energy more effectively.

Sixth Embodiment

Next, a sixth embodiment of the invention is described with particularemphasis on the difference with the first embodiment.

FIG. 7 is a diagram showing the structure of a vehicle powertransmission system according to a sixth embodiment of the invention. InFIG. 7, the reference numerals identical to those in FIG. 1 representthe same elements.

As shown in FIG. 7, this embodiment includes a torque applying device 47which applies torque to the ring gear R coupled to the alternator 32,and a thermal energy recovering system 47 a to recover, by the coolingsystem of the engine 10, the thermal energy generatd when the torqueapplying device 47 applies torque to the ring gear R. The torqueapplying device 47 may be a brake device constituted of a frictionplate, for example.

According to the sixth embodiment, other than the above advantages (1)to (6) provided by the first embodiment, the following advantage can beobtained.

(12) This embodiment includes the torque applying device 47 whichapplies torque to the ring gear R coupled to the alternator 32. Thismakes it possible to supply regenerative energy to the flywheel 30 asnecessary under condition where the power generation control of thealternator 32 cannot be performed, for example, when the auxiliarybattery 36 is in the fully charged state.

(13) The thermal energy generated from the torque applying device 47 isrecovered by the cooling system of the engine 10. This makes it possibleto effectively use the large thermal energy generated when the powergeneration control of the alternator 32 is stopped during energyregeneration control, and the ring gear R coupled to the alternator 32is applied with torque in the direction to stop the rotation of the ringgear R. This thermal energy can be used for space heating of thevehicle.

Seventh Embodiment

Next, a seventh embodiment of the invention is described with particularemphasis on the difference with the first embodiment.

FIG. 8A is a diagram showing the structure of a power transmissionsystem for use in a vehicle according to a seventh embodiment of theinvention. In FIG. 8A, the reference numerals identical to those in FIG.1 represent the same elements.

This embodiment enables using recovered regenerative rotational energyas it is without converting the recovered rotational energy intoelectric energy by the provision of the flywheel 30.

As shown in FIG. 8A, in this embodiment, a first power split device 54is mechanically coupled with the engine 10, a first motor-generator 50 aand a second power split device 58. More specifically, the first powersplit device 54 is constituted of a planetary gear device whose sun gearS is mechanically coupled to the first motor-generator 50 a, whosecarrier C is mechanically coupled to the engine 10 through a lockingdevice 56, and whose ring gear R is mechanically coupled to the secondpower split device 58. The ring gear R is mechanically coupled to thedrive wheels 16 through the differential 14.

The second power split device 58 is mechanically coupled with a secondmotor-generator 50 b and the flywheel 30 in addition to the first powersplit device 54. More specifically, the second power split device 58 isconstituted of a planetary gear device whose sun gear S is mechanicallycoupled to the flywheel 30 through a clutch 60 and the step-up device40, whose carrier C is mechanically coupled to the first power splitdevice 54, and whose ring gear R is mechanically coupled to the secondmotor-generator 50 b. FIG. 8B shows the cross-sectional structures ofthe first and second power split devices 54 and 58.

The first and second motor-generators 50 a and 50 be are electricallyconnected to a high voltage battery 70 respectively through an inverter52 a and an inverter 52 b. The voltage of the high voltage battery 70(several hundred volts) is higher than the voltage of the auxiliarybattery 36 (several volts to over ten volts). The control apparatus 34controls control variables of the first and second motor-generators 50 aand 50 b by manipulating the inverters 52 a and 52 b. The first andsecond motor-generators 50 a and 50 b, the inverters 52 a and 52 b, andthe high voltage battery 70 constitute a vehicle high voltage systeminsulated from the vehicle low-voltage system. Accordingly, the controlapparatus 34 manipulates the inverters 52 a and 52 b through insulatingmeans such as photocouplers.

The second power split device 58, the flywheel 30 and the secondmotor-generator 50 b constitute a mechanical regenerative system MRScapable of storing rotational energy as it is without converting therotating energy into electric energy. Replacing this system with thesecond motor-generator 50 b makes a conventional system for aparallel-series hybrid vehicle.

FIGS. 9A to 9E are collinear diagrams of the rotational speeds of thethree rotating bodies (sun gear R, carrier C and ring gear R) for eachof the first and second power split devices 54 and 58 controlled by thecontrol apparatus 34. In FIGS. 9A to 9E, the arrows indicate thedirections of torque. In these figures, the direction of torque, as wellas the rotational speed, is positive when it points upward. Accordingly,the rotational energy is defined to be positive when it enters the powersplit device. In the following, FIGS. 9A to 9E are explained in thisorder.

FIG. 9A Showing a State in which the Vehicle is Stationary:

When the vehicle is stationary, the rotating bodies of the first powersplit device 54 are stationary. On the other hand, since the flywheel 30stores rotational energy and its rotational speed is not 0, therotational speed of the second motor-generator 50 b is not 0 although itis in the non-drive state. This is because that the rotational speeds ofthe sun gear S, carrier C and ring gear R of the second power splitdevice 58 are on a line in the collinear diagram, and the rotationalspeed of the carrier C coupled to the drive wheels 16 is brought to 0.

FIG. 9B Showing a State in which the Vehicle Starts Moving or Runs UnderLight Load (EV-Running):

In this case, the first motor-generator 50 a and the engine 10 are putinto the non-drive state, and the first power split device 54 does notcontribute to transmission of rotational energy. During this state, thesecond motor-generator 50 b operates as a motor, and the rotationalenergy of the second motor-generator 50 b and the rotational energy ofthe flywheel 30 are supplied to the drive wheels 16.

FIG. 9C showing a state in which the vehicle runs steadily. During thisstate, the engine 10 is caused to run, the first motor-generator 50 a iscaused to operate as a generator, and the second motor-generator 50 b iscaused to operate as a motor. At this time, it is possible to control anamount of the rotational energy supplied from the flywheel 30 to thedrive wheels 16 per unit time by the torque of the second-motorgenerator 50 b. Incidentally, the first motor-generator 50 a can be usedas a motor at this time by bringing the rotational speed of the firstmotor-generator 50 a to the negative area in the collinear diagram.

FIG. 9D Showing a State in which the Vehicle Accelerates:

Also during this state, the engine 10 is caused to run, the firstmotor-generator 50 a is caused to operate as a generator, and the secondmotor-generator 50 b is caused to operate as a motor. At this time, thedrive wheels 16 are driven mainly by the engine 10. However, they areassisted by the second motor-generator 50 b and the flywheel 30 asnecessary at this time. Incidentally, it is preferable to increase theamount of power generation of the first motor-generator 50 a with theincrease of the output of the second motor-generator 50 b in order tosupplement the power consumption of the high voltage battery 70.

FIG. 9E Showing a State in which Power is Regenerated:

During this state, the first motor-generator 50 a and the engine 10 areput into the non-drive state, and the first power split device 54 doesnot contribute to transmission of rotational energy. During this state,the second motor-generator 50 b and the flywheel 30 recover theregenerative energy.

As described above, in this embodiment, in addition to that theregenerative energy is converted into electric energy by the secondmotor-generator 50 b, it is stored in the flywheel 30 in its originalform of rotational energy. Accordingly, according to this embodiment,the regenerative energy usage efficiency can be improved by using therotational energy of the flywheel 30 as drive force when the vehiclestarts moving later.

This is made possible by replacing the second motor-generator 50 b withthe mechanical regeneration system MRS. However, if there occurs powercirculation in the mechanical regeneration system MRS, since energy lossincreases, the energy usage efficiency may be lowered. Accordingly, inthis embodiment, a specific process described in the following withreference to FIGS. 10 to 13 is performed.

FIG. 10A and FIG. 10B are collinear diagrams respectively showing anearly-stage system state and a late-stage system state when regenerativecontrol is performed. When the regenerative control continues, thesystem shifts from the state shown in FIG. 10A to the state shown inFIG. 10E. When the regenerative control continues, the rotational speedof the flywheel 30 continues to increase, while the rotational speed ofthe second-motor generator 50 b continues to decrease. If the rotationalspeed of the second motor-generator 50 b changes in sign, the secondmotor-generator 50 b changes from the regenerative control mode to thepower control mode. As a result, there occurs power circulation in whichthe rotational energy outputted from the second motor-generator 50 b isstored in the flywheel 30.

To prevent the power circulation from occurring, the secondmotor-generator 50 b is put into the non-drive state by lowering therotational speed of the second motor-generator 50 b below a specifiedspeed NL when the rotational speed of the flywheel 30 is positive, andthe first motor-generator 50 a is put under regenerative control asshown in FIG. 10B. By putting the second motor-generator 50 b into thenon-drive state, the second power split device 58 stops contributing topower transmission. At this time, the carrier C of the first power splitdevice 54 is locked by the locking device 56. This is to enable powertransmission through the first power split device 54 while the engine 10is in the non-drive state.

FIG. 11 shows the process of the regenerative control in thisembodiment. This process is repeatedly performed by the controlapparatus 34 at regular time intervals.

This process begins by determining whether or not a regenerative modeprevails in step S10. If the determination result in step S10 isaffirmative, the process proceeds to step S12 to measure the rotationalspeed Nm2 of the second motor-generator 50 b. Subsequently, it isdetermined whether of not the measured rotational speed Nm2 is lowerthan or equal to the specified speed NL. This is for determining whetheror not the power circulation occurs in the mechanical regenerationsystem MRS, causing the energy usage efficiency to be lowered. Thespecified speed NL is set to 0 or negative.

If the determination result in step S14 is negative, the processproceeds to step S16 where the first motor-generator 50 a is put intothe drive state to recover the regenerative energy by the flywheel 30,for example.

On the other hand, if the determination result in step S14 isaffirmative, the process proceeds to step S18 to measure the rotationalspeed Ne of the engine 10. Subsequently, it is determined in step S20whether or not the measured rotational speed Ne is 0. If thedetermination result in step S20 is affirmative, the process proceeds tostep S22 to put the locking device 56 into the engaged state so that thefirst motor-generator 50 b is put under the regenerative control in stepS24.

If the determination result in step S10 or S20 is negative, or when stepS16 or S24 is completed, the process is terminated.

FIGS. 12A and 122 are collinear diagrams showing a system state in anEV-running mode in which the vehicle runs without using the engine 10.When the vehicle runs using the rotational energy of the secondmotor-generator 50 b and the flywheel 30, the rotational speeds of thesecond motor-generator 50 b and the flywheel 30 changes from the onesshown in FIG. 12A to the ones shown in FIG. 122. That is, the speeds ofthe second motor-generator 50 b and the flywheel 30 decrease graduallywhile the vehicle runs using the rotational energy of the secondmotor-generator 50 b and the flywheel 30. If the rotational speed of thesecond motor-generator 50 b changes in sign thereafter, the secondmotor-generator 50 b is put under the regenerative control, and thereoccurs the power circulation in which the rotational energy of theflywheel 30 is supplied to the second motor-generator 50 b.

Accordingly, as shown in FIG. 12B, the second motor-generator 50 b isput into the non-drive state if the rotational speed of the secondmotor-generator 50 b becomes lower than a specified speed Nmth. Further,the first motor-generator 50 a is put under the power control to drivethe vehicle.

The above process is explained in the following with reference to theflowchart of FIG. 13. This process is performed by the control apparatus34 at regular time intervals.

This process begins by determining whether or not the vehicle is runningin the EV running mode in step S30. If the determination result in stepS30 is affirmative, the process proceeds to step S32 to measure therotational speed Nf of the flywheel 30. Subsequently, it is determinedin step S34 whether or not the measured rotational speed Nf is higherthan or equal to a specified speed Nfth. Step S34 is for deter miningwhether or not the rotational energy of the flywheel 30 is sufficient todrive the vehicle. If the determination result in step S34 isaffirmative, the process proceeds to step S36 to measure the rotationalspeed Nm2 of the second motor-generator 50 b. Subsequently, it isdetermined in step S38 whether or not the measured rotational speed Nm2is lower than or equal to the specified value Nmth. Step S38 is fordetermining whether or not the energy usage efficiency decreases if thesecond motor-generator 50 b is driven. If the determination result instep S38 is negative, the process proceeds to step S40 to drive thesecond motor-generator 50 b to use the rotational energy of the flywheel30 as vehicle driving energy.

On the other hand, if the determination result in step S38 isaffirmative, the process proceeds to step S42 to measure the rotationalspeed Ne of the engine 10. Subsequently, it is determined in step S44whether or not the measured rotational speed Ne is 0. If thedetermination result in step S44 is affirmative, the process proceeds tostep S46 to put the locking device 56 in the engaged state. Thereafter,the process proceeds to step S48 to perform the power control by thefirst motor-generator 50 a.

If the determination result in step S30 or S44 is negative, or when stepS40 or S48 is completed, the process is terminated.

The system states in this embodiment are not limited to the onesdescribed with reference to FIGS. 9A to 9E. There are other systemstates shown in FIGS. 14A to 14E explained in the following, forexample.

FIG. 14A Showing a State in which the Vehicle has Been Stopped for aLong Time:

In this case, to prevent the rotational energy of the flywheel 30 fromgradually decreasing, the second motor-generator 50 b is put under theregenerative control. At this time, the carrier C of the second powersplit device 58 is locked because the brake is being applied and thedrive wheels 16 are locked.

FIG. 14B Showing a State in which the Vehicle is Stopped with theRemaining Capacity (SOC) of the High Voltage Battery 70 Being Small:

In this case, the engine 10 is put into the drive state, and therotational energy of the engine 10 is recovered through the regenerativecontrol of the first motor-generator 50 a. The thus recovered energy isused to charge the high voltage battery 70. However, when the remainingcapacity of the auxiliary battery 36 is small, the recovered energy maybe used to charge the auxiliary battery 36 through a step-down converter36 (not shown).

FIG. 140 showing a state in which the rotational energy of the flywheel30 is not sufficient to start the engine 10:

In this case, the first motor-generator 50 a is put under the powercontrol in order to provide an initial rotation to the crankshaft 10 aof the engine 10.

FIG. 14D Showing a State in which the Vehicle Runs Backward:

In this case, the first motor-generator 50 a is put under the powercontrol in a state where the engine 10 is stopped, and the carrier C ofthe first power split device 54 is locked by the locking device 56. As aresult, the rotational speed of the ring gear R of the first power splitdevice 54 can be made equal to the speed of the drive wheels 16 rotatingreversely.

The seventh embodiment described above provides the followingadvantages.

(14) The second motor-generator 50 b mounted on a parallel-series hybridvehicle, which operates to distribute the powers of the first and secondmotor-generators 50 a and 50 b and the engine 10, is replaced by themechanical regeneration system MRS. This makes it possible to improvethe usage efficiency of the regenerative energy, because theregenerative energy can be stored in its original form of mechanicalenergy.

(15) There is provided the locking device 56 to lock the carrier Ccoupled to the engine 10. This enables power transmission through thefirst power split device 54 even when the engine 10 is in thenon-operating state.

(16) If the power circulation occurs between the flywheel 30 and thesecond motor generator 50 b, the second motor-generator 50 b is stopped,and the regenerative control is performed using the firstmotor-generator 50 a in a state where the carrier C of the first powersplit device 54 is locked by the locking device 56. This makes itpossible to suppress the energy usage efficiency from being lowered.

(17) When the vehicle runs in the EV-running mode, it is determinedwhether or not the second motor-generator 50 b should be driven based onthe rotational speed of the flywheel 30. This makes it possible toeffectively use the rotational energy of the flywheel 30.

(18) If the power circulation occurs between the flywheel 30 and thesecond motor generator 50 b when the vehicle runs in the EV-runningmode, the second motor-generator 50 b is stopped, and the regenerativecontrol is performed using the first motor-generator 50 a in a statewhere the carrier C of the first power split device 54 is locked by thelocking device 56. This makes it possible to suppress the energy usageefficiency from being lowered.

(19) There is provided the clutch 60 to disengage the mechanicalcoupling between the sun gear S and the flywheel 30. This makes itpossible to interrupt power transmission between the second power splitdevice 58 and the flywheel 30.

(20) Between the sun gear S and the flywheel 30, there is interposed thestep-up device 40. This makes it possible to make the flywheel 30compact in size compared to the case where the step-up device 40 is notinterposed for the same energy storing capacity.

Modifications of the First to Sixth Embodiments

Regarding the configuration of the mechanical coupling between the powersplit device 24 and the flywheel 30: In each of the above embodiments,the flywheel 30, engine 10 and alternator 32 are respectivelymechanically coupled with the sun gear S, carrier C and ring gear R ofthe power split device 24 constituted of a planetary gear device.However, the configuration of the mechanical coupling between the powersplit device 24 and the flywheel 30 may be such that the alternator 32,engine 10 and flywheel 30 are respectively mechanically connected withthe sun gear S, carrier C and ring gear R of the power split device 24constituted of a planetary gear device.

Regarding the Structure of the Power Split Device 24:

The power split device 24 is not limited to the one constituted of asingle planetary gear device. For example, it may be constituted of thefirst power distributing device 54 shown in FIG. 8 and the second powerdistributing device 58 shown in FIG. 8. Also in this case, if a clutchis disposed between the first and second power distributing devices 54and 58, the same advantage as the above described advantage (1) providedby the first embodiment can be provided. For another example, it may beconstituted of a pair of power split devices, two of the sun gear,carrier and ring gear of one of the power split devices beingrespectively mechanically coupled to two of the sun gear, carrier andring gear of the other power distributing device. In this case, thereexist four rotating bodies having different rotational speeds on thecollinear diagram, and three of them are coupled respectively to theflywheel 30, engine 10 and alternator 32.

Alternatively, two of the four rotating bodies may be respectivelycoupled to different alternators or different flywheels. In this case,by coupling the rotating bodies of a specific one of the planetary geardevices to a flywheel and two alternators, it becomes possible totransmit power between the flywheel 30 and the alternators even when thelock device 22 is not provided. Further, in the case where the three ofthe four rotating bodies of the specific planetary gear device arerespectively coupled to the engine 10 and the different alternators, itis possible to transmit power between the engine 10 and the alternatorsthrough the power split device even when the lock device 26 is notprovided.

The power split device 24 is not limited to the one constituted of aplanetary gear device. For example, it may be constituted of adifferential gear device.

Regarding the Vehicle-Mounted Accessories Driven by the Power SplitDevice 24:

Such accessories are not limited to the compressor 44 and vacuum pump 45of the vehicle air conditioner. For example, only one of the compressor44 and vacuum pump 45 may be driven by the power split device 24. Awater pump to circulate the cooling water of the engine 10 may be drivenby the power split device 24. Further, an oil pump to circulatelubricating oil may be driven by the power split device 24.

Regarding the Electric Rotating Machines Whose Outputs are Distributedby the Power Split Device 24:

Such electric rotating machines are not limited to the alternator 32 andthe starter 18. Such electric rotating machines may include amotor-generator. In this case, the motor-generator may be put below thepower control at the time of starting the engine, running in theEV-running mode, accelerating the vehicle, or regenerating energy.Preferably, such a motor generator is applied with the voltage of thevehicle-mounted high voltage battery insulated from the auxiliarybattery 36.

Other Modifications

The first to fourth and sixth embodiments may be modified such that thetransmission 12 is disposed between the engine 10 and the power splitdevice 24.

The third to sixth embodiments may be modified in the same way in whichthe second embodiment is modified from the first embodiment.

The fourth to sixth embodiments may be modified in the same way in whichthe third embodiment is modified from the first embodiment.

The fifth and sixth embodiments may be modified in the same way in whichthe fourth embodiment is modified from the first embodiment.

The sixth embodiment may be modified in the same way in which the fifthembodiment is modified from the first embodiment.

The first embodiment can provide the foregoing advantage (1) even whenit does not include the clutch 28.

The section (i) of FIG. 2A shows the case where the alternator 32converts the rotational energy stored in the flywheel 30 into electricenergy when the vehicle is stationary. However, when it is expected thatthe vehicle will start before long, the rotational energy stored in theflywheel 30 is not necessary to be converted into electric energy by thealternator 32 in order to use the rotational energy of the flywheel 30as driving force of the drive wheels 16 while preventing occurrence ofenergy loss due to conversion of the rotational energy to electricenergy. Incidentally, the condition where it is preferable not toperform the power generation control of the alternator 32 when thevehicle is stationary includes the one in which the engine isautomatically stopped by idle-stop control.

Modifications of the Seventh Embodiment

Regarding the Configuration of the Coupling Between the Second PowerSplit Device 58 and the Flywheel 30:

The seventh embodiment may be modified such that the sun gear S iscoupled to the second motor-generator 50 b, and the ring gear R iscoupled to the flywheel 30. Regarding the configuration of the couplingbetween the first power split device 54 and the first motor-generator 50a: The seventh embodiment may be modified such that the sun gear S iscoupled to the second power split device 58, and the ring gear R iscoupled to the first motor-generator 50 a.

Regarding the First and Second Power Split Devices 54 and 58:

They are not limited to the one constituted of a planetary gear device.For example, they may be constituted of a differential gear.

Between the clutch 60 and the second power split device 58, a lockingdevice may be disposed in order to enable power transmission through thesecond power split device 58 under condition that the flywheel 30 isinhibited to rotate.

The clutch 60 might not be provided.

The step-up device might not be provided.

Between the first and second power split devices 54 sand 58, a clutchmay be disposed.

The carrier C of the first power split device 54 may be locked by thelocking device 56 in the early stage of the regenerative control shownin FIG. 10A in order to prevent the engine 10 from rotating togetherwith the carrier C of the first power split device 54.

The carrier C of the first power split device 54 may be locked by thelocking device 56 in the early stage of the EV-running mode shown inFIG. 12A in order to prevent the engine 10 from rotating together withthe carrier C of the first power split device 54. Common modificationsof the first to seventh embodiments

Regarding the Speed Step-Up Means:

The speed step-up means constituted of a single planetary gear device isnot limited to the one in which the ring gear R is locked. For example,it may be the one in which the carrier C is locked. In this case, it ispreferable to couple the flywheel to the sun gear.

Further, the speed step-up means is not limited to the one constitutedof a single planetary gear device. For example, it may be the oneconstituted of a single differential gear.

Regarding the Planetary Gear Device:

The planetary gear device is not limited to the one in which therotational speed of the ring gear R and the rotational speed of the sungear S have to be different from each other in sign to satisfy thecondition that the rotational speed of the carrier C is 0 when therotational speeds of the ring gear R and the sun gear S are not 0. Itmay be the one in which the condition can be satisfied when therotational speed of the ring gear R and the rotational speed of the sungear S are the same in sign. Such a planetary gear device is known as“double planetary gear device”. For example, refer to Japanese PatentApplication Laid-Open No. 2001-108073.

The above explained preferred embodiments are exemplary of the inventionof the present application which is described solely by the claimsappended below. It should be understood that modifications of thepreferred embodiments may be made as would occur to one of skill in theart.

1. A power transmission system for use in a vehicle comprising: a powersplit device to perform power distribution among a flywheel for storingrotational energy as mechanical energy, an internal combustion engineand an electric rotating machine; and an interrupting device tointerrupt power transmission between a group of the flywheel and theelectric rotating machine and a group of the internal combustion engineand drive wheels of the vehicle when rotational energy stored in theflywheel is transmitted to the electric rotating machine through thepower split device under condition that power is transmitted between theinternal combustion engine and the drive wheels.
 2. The powertransmission system according to claim 1, wherein the power split deviceincludes a first rotating body mechanically coupled to the flywheel, asecond rotating body mechanically coupled to the internal combustionengine, and a third rotating body mechanically coupled to the electricrotating machine, rotational torques of the first to third rotatingbodies being in a linear relationship.
 3. The power transmission systemaccording to claim 2, wherein the interrupting device includes a clutchto disengage mechanical coupling between the internal combustion engineand the second rotating body, and the power split device furtherincludes a rotation restricting device to restrict the second rotatingbody from rotating.
 4. The power transmission system according to claim3, further comprising a clutch to disengage mechanical coupling betweenthe first rotating body and the flywheel.
 5. The power transmissionsystem according to claim 4, wherein the power split device includes arotation restricting device to restrict the first rotating body fromrotating.
 6. The power transmission system according to claim 2, whereinthe first rotating body is mechanically coupled to the flywheel througha speed-up device to increase rotational speed of the first rotatingbody.
 7. The power transmission system according to claim 2, wherein thepower split device includes a rotation restricting device to restrictthe third rotating body from rotating.
 8. The power transmission systemaccording to claim 7, further comprising a thermal energy recoveringsystem to recover thermal energy generated from the rotation restrictingdevice.
 9. The power transmission system according to claim 2, whereinthe third rotating body is mechanically coupled to a vehicle-mountedaccessory in addition to the electric rotating machine.
 10. The powertransmission system according to claim 9, wherein the vehicle-mountedaccessory is a pressure reducing device to reduce pressure inside ahousing of the flywheel.
 11. The power transmission system according toclaim 2, wherein the electric rotating machine is a vehicle-mountedalternator.
 12. The power transmission system according to claim 11,wherein the third rotating body is mechanically coupled to avehicle-mounted starter in addition to the vehicle-mounted alternator.13. The power transmission system according to claim 11, wherein arotating shaft of the internal combustion engine is mechanically coupledto the power split device at one end thereof, and to the drive wheels atthe other end thereof.
 14. The power transmission system according toclaim 13, wherein a transmission is interposed between the internalcombustion engine and the drive wheels.
 15. The power transmissionsystem according to claim 1, wherein the power split device ismechanically coupled to a coupler between the internal combustion engineand the drive wheels.
 16. The power transmission system according toclaim 15, wherein a transmission is interposed between the internalcombustion engine and the drive wheels.
 17. The power transmissionsystem according to claim 2, wherein the power split device is aplanetary gear device including a sun gear as the first rotating body, acarrier as the second rotating body and a ring gear as the thirdrotating body.
 18. A power transmission system for use in a vehiclecomprising: a first power split device including a first rotating bodymechanically coupled to a first electric rotating machine, a secondrotating body mechanically coupled to drive wheels of the vehicle and athird rotating body mechanically coupled to an internal combustionengine of the vehicle, and configured to perform power distributionamong the first electric rotating machine, the drive wheels and theinternal combustion engine; and a second power split device including afourth rotating body mechanically coupled to a flywheel for storingrotational energy as mechanical energy, a fifth rotating bodymechanically coupled to a second electric rotating machine, and a sixthrotating body mechanically coupled to one of the first to third rotatingbodies of the first power split device to perform power distributionamong the flywheel, the second electric rotating machine and the firstpower split device.
 19. The power transmission system according to claim18, wherein torques of the first to third rotating bodies are in alinear relationship, and the first power split device further includes arotation restricting device to restrict the third rotating body fromrotating.
 20. The power transmission system according to claim 19,further comprising a determining section to determine whether the secondrotating machine should be driven based on rotational speed of theflywheel when the vehicle runs without using power of the internalcombustion engine.
 21. The power transmission system according to claim20, wherein the determining section determines that the second electricrotating machine should not be driven when there is a possibility ofoccurrence of power circulation between the second electric rotatingmachine and the flywheel.
 22. The power transmission system according toclaim 21, wherein torques of the first to third rotating bodies are in alinear relationship, and the power transmission system is configured toperform power control of the first electric rotating machine in a statewhere the third rotating body is restricted from rotating by therotation restricting section if the determining section determines thatthe second electric rotating machine should not be driven.
 23. The powertransmission system according to claim 19, configured to perform powergeneration control of the first electric rotating machine in a statewhere the third rotating body is restricted from rotating by therotation restricting device when power circulation occurs between theflywheel and the second electric rotating machine during decelerationregeneration of the vehicle.
 24. The power transmission system accordingto claim 23, further comprising a determining section to determinewhether the second rotating machine should be driven based on rotationalspeed of the flywheel when the vehicle runs without using power of theinternal combustion engine.
 25. The power transmission system accordingto claim 24, wherein the determining section determines that the secondelectric rotating machine should not be driven when there is apossibility of occurrence of power circulation between the secondelectric rotating machine and the flywheel.
 26. The power transmissionsystem according to claim 25, wherein torques of the first to thirdrotating bodies are in a linear relationship, and the power transmissionsystem is configured to perform power control of the first electricrotating machine in a state where the third rotating body is restrictedfrom rotating by the rotation restricting device if the determiningsection determines that the second electric rotating machine should notbe driven.
 27. The power transmission system according to claim 18,further comprising a clutch to disengage mechanical coupling between theflywheel and the fourth rotating body.